Don't you have a plan to make the creation of coroutine for compressed write in
in block layer? Or will bdrv_co_pwritev gain a "compressed" flag
(BDRV_REQ_COMPRESSED) in the future?

Actually, I already have these patches as part of the issue of backup
compression, hope to send today.

Sounds good. Do you use a new flag for the normal write functions or just
update the existing .bdrv_write_compressed function?

No, I just added a new interface .bdrv_co_write_compressed and removed
the old. As for compatibility with the old interface in the
bdrv_write_compressed will create a new coroutine and called
bdrv_co_write_compressed, how you did it in the vmdk(only now is in
io.c). Maybe it's not the best idea, but it can be discussed.

Also, please base your series on this one to avoid merge conflicts in
vmdk.c. I'm going to apply the series to block-next now as it's fully
reveiwed. I guess you'll effectively need to revert what this patch does
to vmdk_write_compressed() in favour of a block/io.c solution.

Yes, patches will be based on this series, I specifically made sure of it :)